Ranging is a procedure by which a mobile station adjusts transmission parameters (frequency offset, time offset and transmit power) for uplink communication with a base station when the mobile station performs network re-entry and network entry.
Specifically, a ranging procedure is used for the following four purposes: initial ranging, handover ranging, periodic ranging and bandwidth request ranging. Initial ranging refers to a process of uplink time synchronization (i.e., time and frequency synchronization) when a user equipment attempts initial network entry. Handover ranging refers to a process of establishing initial synchronization between a user equipment and a target base station when the user equipment hands over from a source base station to the target base station. Periodic ranging is used for a user equipment to periodically update uplink synchronization. Bandwidth request ranging is used for a user equipment to request an uplink resource to a base station.
When a mobile station attempts to enter a network, the mobile station selects a ranging channel, selects a ranging code, and transmits the selected ranging code to a base station through the selected ranging channel. Upon receipt of the ranging code, the base station transmits, to the mobile station, a message representing that the ranging code has been successfully received.
The number of mobile stations entering a network increases as communication technologies develop. When lots of mobile stations in an idle state attempt network entry/re-entry, access collision and access congestion occur, resulting in deterioration of communication performance. Accordingly, a method for solving this problem is needed.